Figure 2
From: DNA methylation in schizophrenia: progress and challenges of epigenetic studies
Cytosine modification pathways. Recent research has revealed that cytosine modifications can be changed dynamically. DNA methyltransferases (DNMTs) catalyze the conversion of cytosine to 5-methylcytosine (5mC). Ten-eleven translocation (TET) proteins catalyze the synthesis of 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) or 5-carboxylcytosine (5caC). Both 5fC and 5caC are thought to be replaced by cytosine by DNA repair processes such as base excision repair. Thus, 5hmC, 5fC and 5caC are thought to be intermediate products of demethylation. The synthesis of 5-hydroxymethyluracil (5hmU) or thymine is thought to be catalyzed by activation-induced deaminases/apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like (AID/APOBEC) cytidine deaminases from 5hmC or 5mC, respectively. However, recent studies have questioned these reactions [131].